Place stock in a bowl and sprinkle with gelatin. Set aside. Purée tomatoes in the can using an immersion blender.

Heat olive oil in a large Dutch oven over high heat until shimmering. Add ground beef, pork, and lamb; season with salt and pepper; and cook, stirring and breaking up with a wooden spoon or potato masher, until no longer pink, about 10 minutes. Remove from heat.

Meanwhile, finely chop vegetables in food processor.

Heat butter and pancetta in skillet over medium-high heat, stirring frequently, until fat has rendered but not brown. Add onion, carrots, celery, garlic, sage, and half of parsley and cook, until vegetables are softened but not brown. Transfer mixture to Dutch oven with meat mixture.

Return Dutch oven to high heat and cook, stirring, until most of the liquid has evaporated from the pan, about 10 minutes longer.

Add wine and cook, stirring, until mostly evaporated. Add reserved stock, tomatoes, milk, and bay leaves. Season gently with salt and pepper.

Bring to a simmer. Cook until liquid has reduced and sauce is rich and thick, an hour

Stir in heavy cream, fish sauce, and remaining parsley. Bring to a boil on stovetop, stirring constantly to emulsify. Season with salt and pepper